Management of adenocarcinoma in situ (ACIS) of the uterine cervix is controversial and cervical conization has been proposed as conservative management in patients desirous of future fertility. The efficacy of conization as treatment for cervical ACIS is unproven, as is the ideal method of follow-up. The purpose of this study was to assess the adequacy of conization of the cervix as conservative management of ACIS, and to assess the ability to detect recurrent disease. Between January 1964 and August 1993, 28 patients with a diagnosis of ACIS made by cone biopsy were seen at Memorial Sloan-Kettering Cancer Center. Initial management was as follows: total abdominal hysterectomy, 11 (39%); radical hysterectomy, 2 (7%); repeat conization, 6 (21%); and close follow-up, 9 (32%). Of the 8 patients with positive margins who underwent a repeat cone biopsy or hysterectomy, 3 had residual ACIS in the subsequent surgical specimen and 1 patient was diagnosed with invasive adenocarcinoma. Four of 10 (40%) patients with negative margins who underwent hysterectomy or repeat cone biopsy had residual ACIS. In addition, one patient whose cone margins were inevaluable was found to have invasive adenocarcinoma in a repeat conization specimen. Fifteen patients were managed conservatively with repeat conization of the cervix or close follow-up. Seven of 15 (47%) have had a recurrent glandular lesion detected after conization; 2 of these recurrences have been invasive adenocarcinoma. Since ACIS is not reliably diagnosed by cervical cytology and colposcopy, patients undergoing conservative management have been typically followed by endocervical curettage (ECC) in combination with Papanicolaou smear. In our series, the ECC was positive in only 43% of patients with glandular lesions prior to conization of the cervix. This retrospective study raises questions about the safety of therapeutic conization as conservative management of patients with ACIS of the uterine cervix and also highlights the potential inadequacy of following patients with Pap smears in combination with ECC.